The present application is directed to a process and apparatus for treating of a heat treatable strap-like material by heating the same to a particular temperature as it is passed through a heat zone. In particular, the process and apparatus are advantageously used for heat treating of a ferrous metal product by raising the temperature thereof to a temperature in the range of about 800.degree. to 1600.degree. F. The process and apparatus result in precision heating of the material being treated by heating the same using high intensity infrared radiation in a controlled environment where the amount of heat input to the strap can be closely controlled.
Infrared radiation and particularly high intensity infrared radiation can be produced by elongate tubes as manufactured by General Electric and a number of applications have been suggested for this radiation as outlined in a Research Inc. brochure, entitled "Infrared Radiant Heat Invisible Tool for Today's Energy Conscience Industry".
In applying infrared radiation in continuous treating of heat treatable strapping and the like, problems occur with respect to lamp burn-out as the life of the lamp rapidly decreases with high operating temperatures and problems occur with respect to the structure for supporting the lamps particularly when a controlled atmosphere is required to avoid oxidization of the metal strap or the like, which is being treated. Heat treating of these products requires the temperture of the product to be raised in a range of 800.degree. to 1800.degree. F. or more and sealing problems between infrared radiation reflecting surfaces occurs due to the extreme temperature range the reflectors are subject to. As mentioned, this problem becomes acute when a controlled atmosphere is required whereby the structure must be designed to keep air and oxygen out of at least a portion of the heat treating zone.
The problems with respect to the operating temperature to which the structure is exposed is overcome in the application of the present process by providing a gas flow through the heat zone sufficient to frequently turn over the atmosphere within the heat zone to remove heat from the structure. In contrast to earlier processes, the atmosphere is frequently turned over to be relatively cool and there is no attempt to directly recycle the heat in the atmosphere back to the material being treated. The cool environment allows a net positive heat flow from the strap or material being treated to the atmosphere. Such an arrangement maintains a cool environment about the strap or product being treated whereby changes in the intensity of the radiation emitted by the lamps, both positive and negative cause a similar change in the energy absorbed by the strap and hence the temperature thereof. This results in a precise process and avoids damage caused by over heating of the strap due to secondary heat sources or due to momentary errors where the intensity emitted by the lamps is too great. It must be recognized that high intensity infrared radiation can rapidly raise the temperature of a thin substrate, such as strap or wire and the like, and, therefore, it is important to be able to have the temperature of the product responsive to positive and negative changes in the radiation emitted by the lamps.
Apparatus of the present invention discloses a simple structure for treating of the product where infiltration of ambient air is reduced to a point that it does not effect the product being treated. The apparatus provides a flow of inert gas over the product being treated as it is moved through the structure to envelop the strap and thereby avoid oxidization on the surface of the strap. Again, this flow of gas is such that it is at a temperature below that of the product being treated, at least when the product is near its final heat treat temperature where over heating of the strap or product could occur if the radiation emitted by the lamps is momentarily to high. This cool environment allows the temperature of the strap to be responsive to both positive and negative changes in the radiation emitted by the lamps. It can appreciated that when the strap or product is at a temperature much less than the final temperature being sought, it is not as important for the gas flow to be below the temperature of the product as a slight overshoot in the temperature would not be a problem, as it would still be below the final temperature to which the strap is be raised.